The invention relates to a control valve configuration for use in a fuel injector for an internal combustion engine. Configurations of this generic type are disclosed, for example, in U.S. Pat. Nos. 5,460,329 and 5,407,131.
In the case of the control valve configuration according to U.S. Pat. No. 5,460,329, fuel passes as a control fluid through an electromagnetically actuable control valve, which is configured as a slide valve, to a pressure intensifier in the injector. Via the electromagnetic activation, at defined times or crank angles of the internal combustion engine the fuel to be injected is placed under high pressure by the pressure intensifier. The fuel which is placed under high pressure then causes, in the conventional manner, the valve needle on the nozzle of the injector to lift off from its seat and to open up the path for the fuel to the nozzle opening, in order to inject the fuel into the combustion chamber of the engine.
Another type of control valve for a fuel injector that operates with a cam-operated pressure-intensifying piston, is described in U.S. Pat. No. 5,407,131. The control valve here is a seat valve that is normally, i.e. in the rest state, open and which can be closed with the aid of a solenoid. In the open state, the fuel delivered from the tank by a lowpressure fuel pump flows back through the control valve to the tank. The fuel injection into the combustion chamber of a diesel engine is initiated by energizing the solenoid, the magnetic force of which brings the seat valve into the closed operating state. The fuel in the injector, which is now no longer able to flow away, is placed under pressure as a consequence of the cam-actuated piston of the pressure intensifier. When the pressure has reached the defined nozzle-needle opening pressure, the injection starts. The injection is ended by deenergizing the solenoid, whereupon the seat valve is re-opened, so that the fuel can flow away again and the pressure in the injector falls.
Leakage and losses which arise due to leaking and as a consequence of the seepage form a problem which generally occurs in the case of control valve configurations for fuel injection and in particular also in the case of the known configurations dealt with above. The sealing function is restricted both in the case of the slide valves and in the case of the seat valves. Slide valves are only inadequately sealed over the sealing gap, and in the case of seat valves, the sealing function is undertaken only in one direction by the seat. Also, relatively long-lasting seepages, for example by keeping open a valve for the control fluid during the rest state, as in the case of the configuration according to U.S. Pat. No. 5,407,131 mentioned above, are to be evaluated as a loss.
It is accordingly an object of the invention to provide a control valve configuration for use in a fuel injector for internal combustion engines which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which losses occurring during use are reduced.
With the foregoing and other objects in view there is provided, in accordance with the invention, a control valve configuration for use in a fuel injector for an internal combustion engine. The control valve configuration contains a housing having a valve chamber, a valve inlet for a fluid which is under pressure, and a valve outlet for hydraulically controlling an injection process at a nozzle of the fuel injector. The valve chamber has a first section, a second section, and a return opening. The housing further has a chamber wall defining a rear of the valve chamber and a seat defining a first part of a seat valve disposed in the first section. An actuating device is disposed in the housing. A valve body is disposed in the valve chamber, and the valve body can be displaced axially by the actuating device. Depending on a position of the valve body, the valve body produces or blocks a fluidic connection between the valve inlet and the valve outlet. The valve body has a first valve section forming a second part of the seat valve disposed between the valve inlet and the valve outlet in the first section of the valve chamber. The seat valve is closed in a rest position of the valve body and is opened in a working position of the valve body. The valve body has a second valve section rigidly connected to the first valve section. The second section of the valve chamber and the second valve section form a slide valve which, in the rest position of the valve body produces a fluidic connection between the valve outlet and the return opening and blocks a fluidic connection between the seat valve and the valve outlet. The slide valve closes the return opening and then starts to produce a fluidic connection between the seat valve and the valve outlet only after the valve body leaves the rest position. The first section of the valve chamber leads through the seat of the seat valve in a direction of flow into the second section of the valve chamber.
Accordingly, the valve body that can be displaced axially in the valve chamber by the actuating device has two rigidly connected sections. A first section of the valve body forms a seat valve between the valve inlet and valve outlet in a first section of the valve chamber, the seat valve being closed in a rest position of the valve body and being opened in a working position of the valve body. A second section of the valve body and a second section of the valve chamber form a slide valve which, in the rest position of the valve body, produces a fluidic connection between the valve outlet and a return opening and blocks the fluidic connection between the seat valve and the valve outlet, and which closes the return opening and then starts to produce a fluidic connection between the seat valve and the valve outlet only after it leaves the rest position.
The control valve configuration according to the invention therefore forms two individual valves which are connected in series and one of which is configured as a seat valve and the other of which is configured as a slide valve. Since, in the rest position of the valve body, the outlet of the valve configuration is cut off from the inlet pressure by the closed seat valve and additionally by the slide valve and is connected to the return opening, the outlet is kept unpressurized in this phase without control fluid flowing as wastage through the configuration. In addition, the leakage losses in this phase remain low as a consequence of the cumulative sealing actions of the seat valve and slide valve (connected one behind the other). Since the seat valve naturally begins to open immediately the valve body leaves the rest position, the space between the valve and the slide valve can already be filled with the inlet pressure before the slide valve, after obstructing the return opening, opens up the path to the outlet, with the result that the pressurization of the outlet takes place abruptly.
The outlet of the control valve configuration according to the invention is therefore particularly well-suited for a hydraulic control of the injection process, in which the injection phase is initiated by transfer of the valve body into the working position and the injection interval is determined by the rest position of the valve body.
In the case of a preferred embodiment, the first section of the valve body is a control piston which slides in a tight-fitting manner in the first section of the valve chamber and on the front side of which, which faces the seat valve, an annular active surface which is exposed to the valve inlet pressure is formed. A control space behind a rear active surface of the control piston is connected to the valve inlet via a feed restrictor and to a return connection via a discharge restrictor that is to be opened by the actuating device. In this connection, flow resistances of the restrictors and a proportion in size between the annular active surface and the rear active surface are dimensioned in such a manner that the valve body moves into the working position when the discharge restrictor is opened and moves into the rest position when the discharge restrictor is closed.
In this embodiment, the control piston is preferably configured in such a manner that when it reaches its working position, it presses in a sealing manner onto an access from the control space to the discharge restrictor. This ensures, within the meaning of the above problem definition, that the seepage losses remain limited to the short transition phase of the control piston from the rest position into the working position.
In accordance with an added feature of the invention, the first section of the valve chamber that contains the control piston has a diameter larger than a diameter of the second section of the valve chamber that forms the slide valve. The seat of the seat valve is formed by a conically shaped housing edge of the housing that is situated at a transition region between the first and second sections of the valve chamber. The front side of the control piston has an annular surface with a central zone that rests in a sealing manner on the seat when the valve body is in the rest position.
In accordance with an additional feature of the invention, the annular surface on the front side of the control piston is a tapering transition area on the valve body connecting the first valve section to the second valve section. The first valve section has a diameter greater than a diameter of the second valve section. The housing has an annular groove with a constricted continuation. The conically shaped housing edge forming the seat of the seat valve is an edge of the housing disposed between the annular groove and the constricted continuation in the valve chamber. The valve inlet leads into the annular groove and the annular groove has a diameter larger than the diameter of the first section of the valve chamber. The constricted continuation of the annular groove forms a control edge for the slide valve at the transition region to the second section of the valve chamber.
In accordance with a further feature of the invention, the second valve section has a further annular groove. The further annular groove has an axial dimension dimensioned in such a manner that it spans a distance between the return opening and the valve outlet in the rest position of the valve body and, after the valve body leaves the rest position, the further annular groove leaves the return opening and at a same time spans a distance between the valve outlet and the constricted continuation of the annular groove.
In accordance with another feature of the invention, the return opening has a control edge that is concurrent with an outer edge of the second section of the valve chamber.
In accordance with a further feature of the invention, the control piston has a flow duct connecting the feed restrictor to the control space. The feed restrictor connects the valve inlet to the flow duct.
In accordance with another added feature of the invention, the discharger restrictor is a flow duct having an entry opening situated on a front of the chamber wall.
In accordance with another additional feature of the invention, the control piston has a stop element disposed on the rear active surface. The stop element, when the control piston reaches the working position, is placed in a sealing manner onto the entry opening of the discharge restrictor.
In accordance with another further feature of the invention, the first valve section is a control piston having a rear face with a bore formed therein. The control piston has an end wall defining an end of the bore. The chamber wall of the housing has a return connection and a discharge restrictor with an entry opening fluidically connected to the return connection. A further piston slides in a tight-fitting manner in the bore of the control piston. The further piston is supported on the chamber wall, and the further piston has a flow duct leading through the further piston to the entry opening of the discharge restrictor. The bore defines a control space formed between the end wall of the control piston and the further piston.
In accordance with an added feature of the invention, the housing has a pressure-equalizing duct leading from a space formed between the rear face of the control piston and the chamber wall to ambient pressure.
In accordance with an additional feature of the invention, the further piston has a front end reaching into the bore and strikes against a back of the bore, sealing off the flow duct leading to the discharge restrictor, when the control piston is in the working position.
In accordance with a further feature of the invention, the actuating device is an electromechanical actuator.
In accordance with another feature of the invention, a ball valve is disposed adjacent the discharge restrictor and the actuating device acts on the ball valve for blocking the discharge restrictor.
In accordance with a yet further feature of the invention, the valve outlet is to be connected to a primary side of a pressure intensifier in order to control a nozzle needle of the fuel injector.
In accordance with a concomitant feature of the invention, the actuating device is a piezo actuator.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a control valve configuration for use in a fuel injector for internal combustion engines, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.